Following a drone clash between China and the United States, it's become even more clear that a set of rules are needed to govern drone behavior.

When a Chinese navy ship seized an American drone, the guidelines that already existed under the Code for Unplanned Encounters at Sea (CUES) were not enough to settle the dispute. The two-year-old CUES, which includes agreement from 21 countries in order to manage various kinds of crises, does not apply to underwater drones.

“Such encounters will plausibly increase, especially given on the one hand the proliferation of drones for military use—in both aerial, surface and subsurface dimensions—and on the other hand, the geopolitical context in the region favoring deon use,” Collin Koh Swee Lean, research fellow with Maritime Security Programme at the S. Rajaratnam School of International Studies at Singapore’s Nanyang Technological University told the South China Morning Post.

Though CUES does not currently apply to drones, it can be amended to include drone relations in an appendix, according to Yan Yan, maritime law expert at the National Institute for South China Sea studies.

Drones are only part of governing increasingly autonomous weapons and other military systems that aren’t directly powered by humans. While drones are directed by an actual person, other autonomous or semi-autonomous weapon systems like the Phalanx, used on American navy ships to target incoming missiles, need some form of governance to manage their independent actions.

Even drones, like the American one seized by the Chinese ship, are used in a low-intensity military mission for surveillance. However, it’s not unlikely that in the near future, armed drones will come to be more commonplace in this region, according to Koh.

So as drones, not to mention armed drones, become more commonplace, while the US moves to use autonomous robots underwater and China builds a great underwater wall of robots, using sea drones, international law governing how all these developments engage with each other will need to be ironed out.